Cathode assembly for electron discharge devices



c. v. I ITTON 2,906,912

cATHoDE AssEMBLY'EoR ELEcTRoN DISCHARGE DEVICES Sept; 29, 1959 Fild Nov.15, 1954 ad lull.;

IN VEN TOR.

N@ mm cATnoDE ASSEMBLY Eon ELEc'TRoN DISCHARGE DEVICES Charles V.Litton, Grass Valley, Calif., assigner to Litton Industries, Inc.,Beverly Hills, Calif., a corporation of Delaware Application November15, 1954, Serial No. 468,956 3 Claims. (Cl. 313-344) This inventionrelates to a cathode assembly for electron discharge devices, and moreparticularly to a telescoped cathode assembly of great rigidity whichemploys a filamentary cathode. Although, in general, the cathodeassembly of the invention may be employed in various types of vacuumtubes, it is particularly useful in multicavity magnetrons which employa lamentary cathode of the biiilar type, and the preferred embodiment ofthe invention will therefore be illustrated and described in connectionwith a vacuum tube of this type.

Filamentary cathodes of the bifllar type are in general well known tothe electron art, and are employed to serve several useful functions.Firstly, utilization of two counter-energized helical filamentssubstantially eliminates the extraneous magnetic eld which is normallygenerated by a single helical wound filament. Secondly, a biiilariilamentary cathode provides a S-terminal centertapped cathode assemblythe central terminal of which may be employed for modulating the ow ofelectrons emitted from the cathode.

Although bilar filaments have heretofore found extensive use in thevacuum tube art in general, their use in the magnetron art has beencomplicated heretofore by several factors. For example, the 3-terminalcathode assemblies utilized in the prior art for mounting filamentarycathodes are unusually lengthy and bulky owing partly to the requirementthat all three of the cathode terminals of a magnetron be well insulatedand spaced from the main housing assembly which constitutes the anodeterminal, and partly from the fact that each of the three terminals mustbe spaced axially from the other two terminals in order to facilitatethe making of electrical connections to the terminals. -In addition, theutilization of a bilar flamentary cathode with its concomitant lengthyterminal assembly intensities the problem of maintaining the cathode ina rigid position relative to the associated magnetron anode.

In the prior art one significant advance has been made which offers atleast a partial solution of the problem set forth above. This prior artstructure involves the use of a pair of concentrically mounted conicalfrustrums for supporting the cathode, the frustrums being so shaped attheir apical ends to present a pair of complementary semicircularterminals for respectively connecting to the two windings of thecathode. This particular form of cathode assembly is disclosed in U.S.Patent No. 2,474,263, issued June 28, 1949 to Charles V. Litton.

Although the aforementioned prior art cathode assembly has beensuccessful in proving the utility of employing bilar ilamentary cathodesin magnetrons, it is nevertheless limited by several inherentdisadvantages. Firstly, the resulting cathode assembly is stillrelatively lengthy owing to the fact that the three cathode terminalsare axially spaced from each other by relatively large distances.Secondly, each of the terminals includes a threaded collar to provide aterminal surface which may be engaged by the corresponding connectingterminals of an associated tube socket. Thirdly, the iilamentary cath-States atent 2 ode is still 'susceptible to vibration owing to therelatively large overall length of the cathode assembly.

The present invention, on the other hand, obviates the above and otherdisadvantages of the prior art cathode assemblies by providing arelatively short 3-terminal cathode assembly of exceptional rigidity and011e in which electrical connection is made directly to the terminalswithout the utilization of additional components. According to the basicconcept of the invention, there is provided a unitary cathode assemblyin which the terminal subassembly includes three concentrically mountedand axially spaced annular terminal members which are telescoped so asto be connectable directly to the elements of an associated tube socketwithout employing any additional collars or sleeves.

More particularly, according to the invention each of the three annularterminal members is of a different size and includes first and secondsleeve-like end regions having different diameters, the end regionsbeing separated by an S-shaped central region which telescopicallyinterconnects the two end regions. The iirst or largest terminal memberis coupled at its large end to the magnetron anode housing through aiirst glass sleeve, and is coupled at its smaller end to the large endof the second or intermediate terminal member through a second glasssleeve. Similarly the smaller end of the second terminal member iscoupled to the large end of the third or smallest terminal memberthrough a third glass sleeve, the smaller end of the third terminalmember being enclosed to define in combination with the other terminalmembers and the associated glass sleeves a hermetically sealed cathodeterminal assembly.

The S-shaped central region of each of the terminal members is sooriented with respect to the large end of the terminal member that aportion of the central region protrudes radially from the magnetron axisa distance larger than the outside radius of the glass sleeve connectedto the largerend of the terminal member. In this manner each of theterminals may be engaged by the elements of an associated tube socketwithout interference from the adjacent glass sleeve.

lit is therefore an object of the invention to provide a 3terminalmagnetron cathode assembly wherein the terminals are formed to provide atelescoped terminal subassembly, yeach pair of adjacent terminals beingseparated by an associated glass sleeve.

Another object of the invention is to provide a relatively short andrigid 3-termina1 cathode assembly in which the terminals are composed ofannular members having sleeve-like end regions of diierent diameters andan S-shaped central region to provide a telescoped terv minal assemblyin which connection can be made to each terminal without interferencefrom adjacent insulative supporting members.

A further object of the invention is to provide a 3-terminal magnetroncathode assembly including a bilar type iilamentary cathode, theassembly including three concentrically mounted and axially spacedannular members which constitute the cathode terminals, each of theannular members being insulatively supported by an associated glasssleeve and having an S-shaped central region which protrudes radiallyfrom the magnetron axis a distance larger than the radial distance fromthe magnetron axis to the external periphery of the associated glasssleeve.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the following description considered in connection with theaccompanying drawing in which one embodiment of the invention isillustrated by wayk of example. It is to be expressly understood,however, that the drawing is for the purpose of illustration anddescription only, and is not intended as a definition of the limits ofthe invention.

With reference now to the drawing, there is shown in the ligure asectional View of a preferred embodiment of a. cathode assembly,according to the invention, which inludes a hermetically sealedvterminal subassembly, generally `designated 1t), and a cathode supportsubassembly, general-lv Vdesignated 1 ;2. for rigidly Supporting andproviding electrical connection to the bilar lamentary cathode of acathode subassembly, generally designated 1 4.

According to the invention, terminal assembly 10, ir1-V c lundes threeannular terminal members 18, 29 and 22, respectively, which arehermetically sealed to and insu-` lativcly separated by two glasssleeves 24 and 26. In addition, the terminal assembly includes a thirdglass SlSYe 2.?5 Whifh iS herhetally Sealed at .one end to terminalmember 22 and at its other end to a magnetron housing member 30, only aportion o f which is shown.

l VEach of terminal members 1,8, 20 and 22 is preferably constructed ofKovar or a similar alloy whose coeicient of Vthermal expansion closelyapproximates that of glass, and'includes two sleeve-like end regions ofdifferent diameters which are separated by a central region having anS-shapedvcross-sectional conrguration. lt wi-ll be noted that thesmaller ends of terminal members Y22 and 251), are substantiallyidentical in size with the large ends of ter: minal members2t) and 18V,respectively, thereby perrnitf` ting the luse of cylindrical glasssleeves for nsllltlatvely ihtrhghhs'ctins the fsrhrlihals.- It willalso. be notedV that terr'ninalV member l18 enclosed at its7 smallerend.

Asy shOWlll in the ligure, the 'rshaped central region of, 99h ofthe'rihihel members is, S0 oriented with Speer i9 its. hSs'Ciateflshd.regions that it promises. railinly beyond theexternal periphery of theglass sleeve which is. aed to the lares?? Qld, Qf the ierrhihal member;In this manner a heb@ s clsst ihslhlihgthree cohceiitriclcylihdrietalarrays Qf Gentech Sprihgfs may he utilized fer mal;- ing electricalconnection to Vterminal members 18, and` 2: withopt interferencei fromthe adjacent glass sleeves, and without the utilization of additionalmetal sleeves o r Cellars, as rfequiredih theA prior hrt With referenceto` the iight?, for example; the is illustrated by three conf nectorelements`32, 34 and respectively, how the conlasts. gf e tube Sachet 0fthehove type would engage terminal` members 1 8., ZOand 2,2.,respectively.

The lSIP-shaped central regions ofthe terminal members also serves theadditional function of telescoping the end regions of the terminalmembers, thereby materially de,- creasing the axial length of thecathode assembly of the invention. In practice it has been found thatVcathodeassemblies constructed. in accordance to the principles of theinvention are. several inches shorter than correspondingv cathodeassemblies constructed inr accordance withv the prior ari techniquerIfhe glass sleeves employed for insulatively mountingv terminal'members 18, 20 and 22 are preferably composed of relatively hard glassin order to provide a mechanically rugged'structure capable ofwithstanding4 the relatively hardvacuums established within the chamberdefined byterminal assembly 1Q and the associated magnetron housing. Thelength of glass sleeves 24 and 26 should preferably be such thatadjacent terminal membersl are separated by a distance of the order of.050v of an inch after the terminalY members have been sealed to thesleeves.` Glass sleeve 2,3, on the other hand, IIiust be relatively longinv comparison with the otherr glass!v sleeves, since sleeve 28 must becapable of withstandingVV the` relatively high anode;to cathodepotential normally anche@ i9 hh operating whahah@ A typical' overallliislh for-@ach 0f Sleeves.- Zlf and 2@ is flic) Of anihsh, whileSlew-@.28 is` preferably iB/r inches. le1isth.there. by orcviding.ax`separation between termlrlalmembcr 22'vafllllm'afllh-housingfhffapnrorirhately.- 1V@ taches .Itvvlilllbe'yrecognizedhof course, that the` particular dimens sions selected for thevarious elements of the terminal assembly are determined in view of thedesired position of cathode subassembly 14 relative to the magnetronanode and by the dimensions of the elements of cathode supportsubassembly 12.

Cathode support subassembly 12 includes three supporting members 38, 40and 42 for electrically interconnecting terminal members 18, 20 and 22,respectively, with cathode subassembly 14 and for rigidly maintainingthe position of the cathode relative to the associated magnetron anode,not shown. Supporting members 40 and 42 are preferably two conicalfrustrums constructed in accordance with the principles disclosed in theaforementioned Patent 2,474,263 to Charles V. Litton, and are sodisected to provide at their apicalends two spaced, conjugate,semicircular supports which are connected to the left hand end of thecathode subassembly, as viewed in the ligure. Supporting members 4l) and42 are preferably constructed of molybdenum or a similar material havinga relatively low coefficient of thermal expansion, and are aflixed atthe periphery of their larger ends to terminal members 20 and 22,respectively, as by brazing, for example. Supporting member 38 ispreferably composed of a hollow rod of molybdenum or a similar material,and is brazed at one end to terminal member 18, the other end ofsupporting member 3S having a shouldered hole bored therein to provide arecess for receiving a cooperating element of cathode subassembly 14.The holes 44 and 46 bored through supporting member 38 are provided toinsure that the interior of the member is also evacuated when themagnetron employing the cathode assembly of the invention is outgassedor exhausted.

Cathode sub-assembly 14 includes a bililar type filamentarycathodehaving two helical windings which are designated 50` and 5:1,respectively, the right hand end of each winding, as viewed inthe-ligure, being' electrically and mechanically connected to a commonconnecting memberSZ. This connecting member is, in turn, xedly attachedas by welding or brazing, to a center rod 54 which is composed oftungsten, for example, the center rod being seated in and rigidly heldby the central supporting member 38. As shown in the ligure, connectingmember 52 may be grooved to improve its heat-dissipating properties.

The other ends of cathode windings 50 and 51 are respectively connectedto two semicylindrical connecting members 56 and Sil-which, in turn, arebrazed to the api# cal ends of supporting members 40 and 42,respectively. Connecting members 56 and 58 are preferably constructed ofmolybdenum and, as shown in the ligure, arev spaced from center rod 54and from each other by finite distances in order to prevent shortcircuiting of the cathode windings.

Connecting member 56 also includes a shoulder 60 which is utilized forlixedly supporting an annular endhat member 62, the end-hat member beingspaced from connecting member 58 and including a flanged end 64 forrestricting to a predetermined region thel electron emission into themagnetron interaction chamber. The left hand end of` connecting member52, as shown in the ligure, is also llanged to provide a second end-hatfor restricting the effective region of emission at the other end of thecathode. Both end-hat 62 and connecting member 52 are preferablyconstructed of zirconium coated molybdenum with a platinum coating overtheir flanged portions.

It will be. recalledzthat connecting members 56 and 58 are spaced fromeach other and from center rodi54 in order to,l prevent short circuitingof 'one or both of the cathode windings. It has been found that duringoperation ofthe magnetron there may be a tendency for free electrons` topass through the slot between connecting members 56 and 58` and energizestructural parts of the magnetron other than the anode, thereby tendingto generate oscillations atan undesired frequency. Accordingly, theleft-handvendof end-hat memberA 62; as viewedl in the figure, isextended axially along connecting mem'- bers 56 and 58 a distancesuicient to prevent the emission of electrons from the slottherebetween.

As set forth hereinabove the cathode comprises two lamentary windings Sand 51 which are so mounted and enengized as to constitute a biilarfilament. The windings are preferably constructed of carburizedthoriated tungsten and are energized so that current in adjacent turnslows in opposite directions with the result that the magnetic fieldproduced by the cathode current is substantially neutralized.Accordingly, if alternating current is applied to energize the cathode,-as is often the case in practice, the small amount of residualalternating flux produced by the cathode is insufficient to appreciablymodulate the electrons emitted from the cathode.

In operation power for energizing the lamentary cathode is applied toterminals 20 and 22 to energize the two cathode windings in series. Itwill be recognized, therefore, that terminal 18 and its associatedsupporting and connecting members constitute a cathode center tap whichmay be utilized, if desired, to modulate the electron emission from thecathode windings.

It will be recognized from the foregoing description that the presentinvention provides a rigid 3-termina1 magnetron cathode assembly whichis relatively compact and in which electrical connection may be madedirectly to each of the three terminals without the utilization ofadditional components. In addition, it will be recognized that theutilization of a telescoped terminal subassembly foreshortens the entirecathode assembly and functions to materially increase the rigidity ofthe overall structure while simultaneously decreasing the sensitivity ofthe cathode assembly to temperature changes.

What is claimed as new is:

l. A cathode assembly for an ultra-high frequency electron dischargedevice, said cathode assembly cornprising: a biilar lilamentary cathodeincluding rst and second helical windings each having first and secondends; a terminal subassembly including iirst, second and third annularterminal members having a common axis, rst and second insulative sleevesinsulatively interconnecting and concentrically mounting said rst andsecond terminal members with said second and third terminal members,respectively, and a third insulative sleeve insulatively interconnectingsaid third terminal member with the housing of the electron dischargedevice, each of said terminal members including two end regions ofdiierent diameters interconnected by a telescoped S-shaped centralregion a portion of which reverses direction with respect to said commonaxis, the smaller ends of said second and third terminal members beingsubstantially equal in diameter with the llarger ends of said first andsecond terminal members, respectively, said S-shaped central region ofeach of said terminal members protruding radially from the common axisof said members a distance larger than the outside radius of the glasssleeve which is connected to its larger end region to provide aprotruding annular contact surface adopted to engage a contact member ofan associated tube socket; and means connected to said terminal membersand to said lilamentary cathode for mechanically mounting said cathodeand electrically interconnecting said cathode windings to said terminalmembers.

2. In a cathode assembly for utilization in a vacuum tube generator ofultra-high frequency electrical signals, a terminal subassembly forproviding external electrical connection to an internally mountedcathode, said terminal subassembly comprising: rst, second and thirdannular terminal members, each of said membersI including a large endregion and a small end region telescopically interconnected by a centralregion said central region having an S-shaped cross sectionalconfiguration a portion of which reverses direction with respect to saidend regions, the larger ends of said rst and second terminal membershaving diameters substantially equal to the diameters of the smallerends of said second and third terminal members, respectively; first andsecond glass sleeves insulatively interconnecting the larger ends ofsaid rst and second terminal members to the smaller ends of said secondand third terminal members, respectively, and a third glass sleeveinsulatively interconnecting the larger end of said third terminalmember to the housing of the vacuum tube generator, said terminalmembers and said glass sleeves being concentrically mounted about acommon axis and said S-shaped central region of each of said terminalmembers protruding radially from said common axis a distance larger thanthe outside radius of the glass sleeve which is connected to itsassociated end region to provide a protruding annular contact surfaceadopted for engagement by a terminal of an associated tube socket.

3. A cathode assembly hermetically sealed to the anode housing member ofa magnetron, said cathode assembly comprising: a cathode element havingfirst, second and third terminals for receiving electrical energy; aterminal subassembly hermetically sealing the anode housing member andproviding external electrical connection to said cathode element, saidterminal subassembly including r.lirst, second and third annularmembers, each of said terminal members including a large end region anda small end region telescopically interconnected by a central region,said central region having an S-shaped cross sectional configuration aportion which reverses direction with respect to said end regions, thelarger ends of said rst and second terminal members having diameterssubstantially equal to the diameters of the smaller ends of said secondand third terminal members, respectively, rst and second glass sleevesinsulatively interconnecting the larger ends of said rst and secondterminal members to the smaller ends of said second and third terminalmembers, respectively, and a third glass sleeve insulativelyinterconnecting the larger end of said third terminal member to theanode housing member, said terminal members and said glass sleeves beingconcentrically mounted about a common axis, the portion of said S-shapedcentral region adjacent the larger end of each of said terminal membersprotruding radially a distance larger than the outside diameter of the'glass sleeve connected to said larger vend to provide a protrudingannular contact surface adapted for engagement by a terminal of anassociated tube socket; and rigid supporting means connected betweensaid first, second and third terminal members and said rst, second andthird terminals ofsaid cathode, respectively, said supporting meanstxedly maintaining the position of said cathode relative to the anodehousing member and being electrically conductive whereby the applicationof electrical signals to said terminal members electrically enengizessaid cathode.

References Cited in the tile of this patent UNITED STATES PATENTS2,455,381 Morton et al. Dec. 7, 1948 2,471,424 Glauber May 31, 19492,474,263 Litton June 28, 1949 2,542,639 De Walt Feb. 20, 1951 2,609,522Hull Sept. 2, 1952 2,634,384 Ford et al. Apr. 7, 1953 2,705,294 ShraderMar. 29, 1955

